I have a 98 windsong with dual air. In the master bedroom there are two wall switches that control the two a/c. I have no instructions on how to use them. Currently I can on run one a/c at a time depending on how I have the switches set. Both units have their own wall mounted thermostats. Thanks for any help.

Sounds like they're On / Off Power switches. I've never seen anyone do this. Generally there will be a breaker for each in the electrical panel and each AC is controlled by the wall mounted t-Stat. It might be a Harry Homeowner set up of some kind. If you place both switches up will both units work? If not one switch may be bad? You may need to remove the one that doesn't turn anything on and check it for continuity.

Many rigs though the late 90s and into the early 2000s had a power management system for the ACs and higher amperage draw items. Because 50amp supply was not all that prevelant and most RVs had only 30amp supply the power management thingy would automatically select between the two to make sure you didn't over power the 30 amp supply. It would also turn off the AC if you tried to use the microwave on some rigs. It depended on how it was set up. Usually this system is transparent to the owner. I can't be positive if this is what you have or not but it would seem a posibility to me. If you only have 30 amp supply to the rig you cannot run 2 ACs at once.

Thanks for the quick responses. I had not thought about one of the switches being bad. I have been playing around with different switch positions. I thought maybe there was an automatic switching between the units and in some combination this would happen.
NWJeeper has a good point. Yes it is only 30amp. I was wondering about a problem having both on at the same time. I am new to RVing so am still learning the ins and outs. It does not look like an after market hookup but it would be nice to know if in some combination these switches would auto switch between units.
Our first outing was this weekend so we are trying to iron out the kinks. I really appreciate the help.

I have the same setup in my 99 Windsong, there are 2 switches both having 3 positions. The reason for this setup is as mentioned before the 30 amp service.
When pluged into land power you can run only 1 AC at a time, when using generator you can use them both because each AC is wired to seperate legs on the genset.

When pluged into land power; Both switches up is rear AC
Both switches down is front AC

When using the Generator Both switches up you can run both front
and rear at the same time.

Middle switch position is no function, I
use it as a off position when I'm not
using them...

Thanks a lot jaco. I thought I had tried that but I will double check. We pull up stakes here Friday and will check when back on the road again. Thanks, I thought I was the only one with that kind of setup. My service guy wasn't sure how they worked either. I really appreciate the help. As we say in the Navy, "Fair Winds and Following Seas"